How can I assess the quality of a local Buddhist group?

I'm located in the West, and, in my local area, there are several Buddhist groups. I would like to join one of them to be more formal in my commitment to learn about Buddhism. My question is, how do I assess the quality of a local Buddhist group in terms of how close they are to the original teachings of the Buddha? How can I assess if a local Buddhist group, or school, has or hasn't deviated from the original spirit of Buddhism?